Electrochemical device including electrolyte

ABSTRACT

An electrochemical device comprising an electrolyte and at least one electrode plate, the electrochemical device having a metal part constituting the electrode plate or being connected to the electrode plate; the electrolyte comprising a solute and a solvent dissolving the solute; the metal part having an insulating oxide layer for preventing the electrolyte from creeping on at least part of the surface of the metal part.

RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.10/265,698, filed on Oct. 8, 2002, now U.S. Pat. No 7,358,008, which inturn claims the benefit of Japanese Application No. 2001-315913, filedon Oct. 12, 2001, the disclosures of which Applications are incorporatedby reference herein.

BACKGROUND OF THE INVENTION

In recent years, there has been a highly increasing demand forelectrochemical devices for various portable devices and hybrid electricvehicles. A concentrated sulfuric acid aqueous solution, a concentratedalkaline aqueous solution and the like have been used as electrolytes ofelectrochemical devices such as secondary batteries and capacitors.Further, non-aqueous solvents with lithium salt dissolved therein havebeen used as electrolytes of lithium ion secondary batteries. Many ofthe electrolytes cause corrosion of materials or damage to the humanbody because of liquid leakage thereof.

It is thus essential to prevent the liquid leakage of the electrolyte inthe electrochemical device; however the electrolyte has a tendency todiffuse on a metal part. The phenomenon of diffusion of the electrolyteon the metal part is called creeping. M. N. Hull et al. gave thefollowing causes of creeping of the electrochemical device using analkaline electrolyte, in “J. Electrochem. Soc., 124, 3, 332 (1977)”: (i)a decrease in surface tension of the electrolyte due to anelectrocapillary action, (ii) an increase in alkaline concentrationcaused by reduction of oxygen on the interface of three phases formed bythe electrolyte, oxygen and a negative electrode, and (iii) thetransportation of the electrolyte driven by the increasing alkalineconcentration.

When an adhesive is applied to a sealing part of the electrochemicaldevice, with the affinity between the metal part and the electrolytehigher than the affinity between the adhesive and the metal part, theadhesive tends to be separated from the metal part by the action of theelectrolyte. It has thus been difficult to prevent the liquid leakage ofthe electrolyte by the use of an adhesive.

Japanese Laid-Open Patent Publication No. 2000-58031 proposes the use ofa hermetic seal. The hermetic seal has been in wide use for sealingelectronic components as having high insulating properties andair-tightness. Since a thermal expansion coefficient of glass needs tobe coordinated with a thermal expansion coefficient of a metal, however,it has been difficult to design the hermetic seal, limiting metals toexpensive ones that can actually be used.

In a sealing part of a conventional electrochemical device, for example,a metal part having a surface layer made of butyl rubber and a gasketsuch as an O-ring in close contact with the surface layer have beenused. In a capacitor including an electrolyte aqueous solution, acylindrical rubber plug, having a through hole for passage of a currentcollecting terminal, has been used as a component for sealing an openingof a metal case.

However, in the aforesaid methods of physically blocking theelectrolyte, there are required a step of compressing the gasket withthe metal part, a step of caulking the rubber plug with the end of themetal case, and the like. This may hence raise problems of an increasedproduction cost and of limited design of electrochemical devices. In thecase of the capacitor, since a problem may arise that the electrolyteevaporates from the gap between the rubber plug and the currentcollecting terminal to cause an increase in internal resistance,reliable and inexpensive alternative techniques have been required.

Recently proposed has been an electrochemical device produced bystacking in series bipolar electrode plates each comprising a positiveelectrode, a negative electrode and a bipolar current collector carryingthe positive electrode on one face thereof and the negative electrode onthe other face thereof. In the electrochemical device comprising thebipolar electrode plate, it is of importance to prevent a short circuitbetween the electrode plates through the medium of the electrolyte. Forthis reason, Japanese Patent Publication No. 2623311, Japanese Laid-OpenPatent Publication No. 11-204136 and Japanese Patent Publication No.2993069 propose arranging an insulating material or a liquid impermeablematerial on the periphery of the bipolar current collector.

However, in the electrochemical device comprising the bipolar electrodeplate, it is difficult to control the creeping of the electrolyte.Further, as long as a liquid electrolyte is in use, it is also difficultto prevent the transfer of the electrolyte between the electrode platescaused by fall or vibration of the electrochemical device. When theelectrolyte causes occurrence of the short circuit between the electrodeplates, problems of variation in charged state between the electrodeplates, an increase in self-discharge, and the like, may arise.Meanwhile, an extreme reduction in amount of the electrolyte in order toprevent the transfer thereof results in shorter longevity of theelectrochemical device. Accordingly, effective methods for preventingthe short circuit between the stacked electrode plates caused by theelectrolyte have been desired.

In recent times, sealed alkaline storage batteries have been used forpower sources of electric power tools and hybrid electric vehicles.Because this usage necessitates a high-voltage power source, pluralbatteries connected in series are used.

However, a typical alkaline storage battery has: a case to accommodate,together with an electrolyte, an electrode plate assembly comprising apositive electrode plate, a negative electrode plate and a separator;and a sealing plate to seal the opening of the case. The cases and thesealing plates in number equivalent to the number of the batteries to beconnected in series are thus needed, which is uneconomical. It istherefore considered that an effective manner is parting the inside of aclosed-bottom resin case into plural spaces, inserting an element forpower generation into each of the isolated spaces, and connecting inseries the elements for power generation with a lead (lead wire), as inthe case of a lead storage battery.

Compared to sulfuric acid to be used in the lead storage battery,however, an alkaline electrolyte to be used in the alkaline storagebattery is more apt to creep on the surface of the metal part such asthe lead. For this reason, there may be cases in which the elements forpower generation connected in series are short-circuited through themedium of the electrolyte, leading to an increase in self-discharge orto variation in charged state between the elements for power generation.It is thus difficult to apply the structure of the lead storage battery,as it is, to that of the sealed alkaline storage battery.

BRIEF SUMMARY OF THE INVENTION

The present invention proposes, in an electrochemical device, aninsulating oxide layer be arranged on a metal part constituting or beingconnected to an electrode plate for the purpose of preventing creepingof an electrolyte due to an electrocapillary action.

Namely, the present invention relates to an electrochemical devicecomprising an electrolyte and at least one electrode plate, theelectrochemical device having a metal part constituting the electrodeplate or being connected to the electrode plate; the electrolytecomprising a solute and a solvent dissolving the solute; the metal parthaving an insulating oxide layer for preventing the electrolyte fromcreeping on at least part of the surface of the metal part. It ispreferable that as the insulating oxide layer, one that can form achemical bond with the metal part is selected.

It is preferable that the metal part comprises at least one selectedfrom the group consisting of Fe, Ni, Co, Cr, Cu, Al and Pb.

It is preferable that the insulating oxide layer has a specificresistance of not less than 10⁶ Ω·cm.

It is preferable that the insulating oxide layer comprises amorphousglass.

It is preferable that the insulating oxide layer contains at least oneelement selected from the group consisting of Si, B, Mg, Na, K, Al, Ca,Ba, Ti, Y, Cr, Ni and Zr.

It is preferable that the insulating oxide layer has a thickness of notless than 10 μm and not more than 200 μm.

It is preferable that the electrochemical device further comprises,between the metal part and the insulating oxide layer, a metal layercomprising at least one selected from the group consisting of Cr, Ni, Feand Co.

It is preferable that the insulating oxide layer is covered with aninsulating resin layer.

It is preferable that the insulating resin layer comprises at least oneselected from the group consisting of polyolefin, polyether, polyacetaland polycarbonate.

It is preferable that the insulating oxide layer is covered with aninsulating resin layer, and the combination of the insulating oxidelayer and the insulating resin layer forms a sealing structure forsealing the electrolyte.

The present invention is particularly effective in an electrochemicaldevice where the electrolyte is in liquid form or gelated form, thesolute comprises an alkali metal hydroxide, and the solvent compriseswater. It is particularly preferable that the electrolyte is in gelatedform.

While the novel features of the invention are set forth particularly inthe appended claims, the invention, both as to organization and content,will be better understood and appreciated, along with other objects andfeatures thereof, from the following detailed description taken inconjunction with the drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a front view of a lead made of nickel with an insulating oxidelayer arranged thereon.

FIG. 2 is a schematic view of a test apparatus for evaluating creepingof an alkaline aqueous solution.

FIG. 3 is a front view of a steel plate with the insulating oxide layerarranged on the periphery thereof.

FIG. 4 is a vertical-sectional view of Battery A.

FIG. 5 is a vertical sectional view of Battery D.

FIG. 6 is a graph representing the relations between the number ofcharge/discharge cycles and discharge capacity ratios of Batteries D toH.

FIG. 7 is a graph representing the relations between the number ofcharge/discharge cycles and capacity maintenance ratios of Batteries Dto H.

FIG. 8 is a front view (a) and a sectional view (b) of the sealing plateof Battery d.

FIG. 9 is a vertical sectional view of the electrode plate assembly ofBattery I.

FIG. 10 is an oblique view of the electrode plate assembly of Battery I.

FIG. 11 is an oblique view of the case and the sealing plate of BatteryI.

FIG. 12 is a vertical sectional view of Battery J.

FIG. 13 is a vertical sectional view of the bipolar current collector ofBattery M.

FIG. 14 is a vertical sectional view of part of the electrode plateassembly of Battery N.

DETAILED DESCRIPTION OF THE INVENTION

The present invention requires an insulating oxide layer which isarranged on a metal part in an electrochemical device using anelectrolyte. In the place on the metal plate where the insulating oxidelayer is arranged, the electrolyte is prevented from creeping. Since thecreeping is most remarkable in the case of using an alkalineelectrolyte, the present invention is particularly effective when thealkaline electrolyte is in use. The examples of the alkaline electrolytemay include an aqueous solution containing an alkali metal hydroxidedissolved therein and a non-aqueous solvent solution containing alkalimetal salt dissolved therein.

There is no specific limitation to the metal part on which theinsulating oxide layer is to be arranged. In the electrochemical device,the insulating oxide layer is applicable to all of the metal partsrequiring prevention of creeping of the electrolyte. The insulatingoxide layer can be arranged, for example, on a current collector of anelectrode plate, a lead, a sealing part constituting a terminal, a metalcase and the like.

To the insulating oxide layer, for example, amorphous glass isapplicable. While amorphous glass of various compositions can beapplied, desirable amorphous glass is one containing at least oneelement selected from the group consisting of Si, B, Mg, Na, K, Al, Ca,Ba, Ti, Y, Cr, Ni and Zr. For example, soda lime glass, aluminosilicateglass, alumino-borosilicate glass, borosilicate glass or the like can beused. It is preferable to use alumino-borosilicate glass, pyrex(registered trade mark) glass, porcelain enamel (glass lining) or thelike, as having high alkali resistance. As preferable glass compositionsgiven may be 76 to 86 wt % of SiO₂, 8 to 18 wt % of B₂O₃, 1 to 6 wt % ofAl₂O₃, and 2 to 9 wt % of Na₂O.

Other than the aforesaid amorphous glass, ceramics such as Al₂O₃, TiO₂,Y₂O₃, Gr₂O₃, NiO and ZrO₂ can also be used. These ceramics all have highinsulating properties and are hence suitable for insulation of the metalpart to be applied with electric potentials.

It is preferable that the insulating oxide layer has a thickness of notless than 10 μm and not more than 200 μm. When the thickness is lessthan 10 μm, the insulation is insufficient and there may occur acreeping on the metal part due to a decrease of the surface tension ofthe electrolyte caused by the electrocapillary action. When thethickness of the insulating oxide layer is over 200 μm, a largedistortion occurs on the interface between the metal and the insulatingoxide layer, making the insulating oxide layer easy to be separated inheat cycles or the like.

In order to firmly bond the insulating oxide layer to the metal part, itis preferable that a metal layer comprising at least one selected fromthe group consisting of Cr, Ni, Fe and Co is in advance formed on thesurface of the metal part. The metal layer preferably has a thickness of0.1 to 20 μm.

In the case of using an insulating oxide layer with not very high alkaliresistance, such as glass mainly composed of SiO₂, it is preferable thatthe surface of the insulating oxide layer is covered with an insulatingresin layer with high alkali resistance. The insulating resin layerprevents corrosion of the insulating oxide layer caused by an alkalineelectrolyte. In this case, since the insulating oxide layer isinsulated, separation on the interface between the insulating oxidelayer and the insulating resin layer is not caused by the action of analkaline electrolyte.

As for the insulating resin, polyolefin such as polyethylene,polypropylene or polystyrene; polyether such as an epoxy resin orpolyacetal; polycarbonate; polysulfide such as polyphenylene sulfide; afluorocarbon resin such as polytetrafluoroethylene or polyvinylidenefluoride, or the like, is preferable as they have excellent alkaliresistance.

The insulating oxide layer can form, together with the insulating resinlayer, a sealing structure for sealing the electrolyte. For example, ina cylindrical battery, the sealing structure with excellent reliabilitycan be formed by arranging the insulating oxide layer at the open-end ofthe metal case, arranging the insulating resin layer on the insulatingoxide layer, and fixing a sealing plate at the open-end of the metalcase.

The sealing structure with excellent reliability can be formed also byarranging the insulating oxide layer on a lead to be pulled out from theinside, a part constituting an external terminal, and the like, andarranging the insulating resin layer on the insulating oxide layer.

However, the insulating oxide layer is not for sealing the electrolytelike the conventional hermetic seal, but for preventing the creeping ofthe electrolyte due to the electrocapillary action. It is the insulatingresin layer that serves to seal the electrolyte. Accordingly, adifference in thermal expansion coefficient between the insulating oxidelayer and the metal part is not important, and in a number ofcombinations of metals and insulating oxides, reliability of theinterface-bonding therebetween can be secured. On the other hand,because the conventional hermetic seal is for sealing the electrolyte,the thermal expansion coefficient of the insulating oxide layer and thatof the metal part need to be coordinated, making the design of thehermetic seal difficult, as above described.

As one of embodiments of the present invention given can be anelectrochemical device comprising at least two elements for powergeneration and at least one lead for electrically connecting the atleast two elements for power generation (e.g., a sealed alkaline storagebattery). Each of the elements for power generation comprises anelectrolyte and at least one electrode plate. The electrolyte comprisesa solute and a solvent dissolving the solute. The lead has an insulatingoxide layer for preventing the electrolyte from creeping on at leastpart of the surface of the lead.

In the preferable embodiment, the at least two elements for powergeneration are accommodated in a case in the state of being isolatedfrom each other so as not to be short-circuited, and the opening of thecase is sealed with a sealing plate. The at least two elements for powergeneration are electrically connected with at least one lead, and theinsulating oxide layer is arranged in band-shape on the lead. It is thuspossible to attempt to reduce cost and improve an energy density bymaking plural elements for power generation share the inner space of onecase. It should be noted that in order to make the elements for powergeneration be in the state of being isolated from each other so as notto be short-circuited, for example, each of the elements for powergeneration is accommodated in a small container such as a closed-bottomresin case, which is then accommodated in a bigger case.

The elements for power generation are electrically connected in seriesor parallel with at least one lead and at least part of the lead iscovered with an insulating oxide. It is thereby possible to prevent thecreeping of the electrolyte due to the electrocapillary action.

As one of embodiments of the present invention, an electrochemicaldevice comprising an electrolyte and one or plural bipolar electrodeplates being stacked can further be given. The bipolar electrode platecomprises a positive electrode, a negative electrode and a bipolarcurrent collector carrying the positive electrode on one face thereofand the negative electrode on the other face thereof. The electrolytecomprises a solute and a solvent dissolving the solute. The periphery ofthe bipolar current collector has an insulating oxide layer forpreventing the electrolyte from creeping on the surface of theperiphery.

It is preferable that, when the bipolar current collector is in asubstantially square shape, the insulating oxide layer arranged on theperiphery of the bipolar current collector has a width not more than onetenth of the width of the bipolar current collector.

In the preferable embodiment, the one or plural bipolar electrode platesbeing stacked are interposed between a pair of end electrode plates, andthe peripheral inside of each of the pair of end electrode plates has aninsulating oxide layer for preventing the electrolyte from creeping onthe surface of the peripheral inside. The insulating oxide layerarranged on the periphery of the bipolar current collector and theinsulating oxide layer arranged on the peripheral inside of the pair ofend electrode plates are bonded to each other with an adhesive. Amonopolar electrode plate, having a positive electrode or a negativeelectrode on only one face thereof and the insulating oxide layer on theperiphery thereof, can be used as the pair of end electrode plates.

In the present invention, it is preferable to use a gel electrolyte asthe electrolyte. The use of a gel electrolyte enables prevention oftransfer of the electrolyte caused by a shock of fall of theelectrochemical device or the like. For example, in the case of using analkaline aqueous solution as the electrolyte, cross-linked polyacrylicacid or polyvinylsulfonic acid, the salts thereof or the like ispreferably used as a material for gel formation to gelate theelectrolyte.

It is preferable that the material for gel formation is included in apositive electrode paste layer and a negative electrode paste layer ofthe electrode plate, a separator and the like. In this case, after theelectrode plate assembly including the material for gel formation isaccommodated together with a liquid electrolyte in a case, the materialfor gel formation can be gelated in the battery. To make the materialfor gel formation included in the separator, it is possible that thematerial is gelated first and then applied to the separator.

The amount of the material for gel formation is desirably in the rangeof about 1 to 15 parts by weight per 100 parts by weight of theelectrolyte. When the material for gel formation is in an amount belowthis range, an increase in viscosity of the electrolyte becomesinsufficient; when the material for gel formation is in an amount overthis range, the volume energy density of the battery decreases.

The positive electrode of the alkaline storage battery is produced, forexample, with the use of a positive electrode paste mainly comprisingnickel hydroxide. The negative electrode of the alkaline storage batteryis produced, for example, with the use of a negative electrode pastemainly comprising a hydrogen storage alloy.

When a bipolar electrode plate is produced, for example, a nickel foamsubstrate is filled with the positive electrode paste, which is thenfixed by welding or the like onto one face of a bipolar currentcollector. The positive electrode can also be obtained by applying thepositive electrode paste directly onto one face of the bipolar currentcollector. The positive electrode can also be obtained by providing aporous sintered nickel layer on the surface of the bipolar currentcollector, impregnating nickel nitrate into the sintered nickel layer tobe dried and immersing the whole into an alkaline aqueous solution toconvert the nickel nitrate into nickel hydroxide. The negative electrodeis arranged on the other face of the bipolar current collector.

The positive electrode and the negative electrode are arranged on thebipolar current collector. The periphery of the bipolar currentcollector is left for arrangement of the insulating oxide layer. In theviewpoint of a current collecting efficiency, it is preferable that thepositive electrode and the negative electrode are not arranged on theinsulating oxide layer. As the width of the insulating oxide layerincreases, therefore, the area of the electrode plate decreases.Further, from the viewpoint of a volume energy density, it is preferablethat the bipolar current collector is in a substantially square shape.It is desirable that the periphery for the arrangement of the insulatingoxide layer has a width not more than one tenth of the width of thebipolar current collector. When the width of the periphery exceeds onetenth of the width of the bipolar current collector, the volume energydensity of the battery extremely decreases.

It is preferable that the bipolar current collector comprises Fe or Nifrom the viewpoint of the alkali resistance. For making the bondingbetween the insulating oxide layer and the bipolar current collectorstrong, it is desirable to form a metal layer comprising Cr, Ni, Fe, Coor the like between the bipolar current collector and the insulatingoxide layer.

It is preferable that the electrode plate assembly comprising one orplural bipolar electrode plates being stacked is covered with aninsulating film and then accommodated in a case. For the case used canbe a metal case made of iron or nickel, a resin case mainly composed ofpolyethylene and polypropylene, or the like. Subsequently, therespective leads attached to the negative electrode and the positiveelectrode of the electrode plate assembly are electrically connected tothe respective external terminals and the sealing plate is attached tothe open edge of the case, to seal the opening of the case.

Below, specific examples of the present invention will be described indetail; however, the present invention is not limited to those examples.

Sample 1

In the following procedure, a glass layer 12 as an insulating oxidelayer was formed on a Ni lead 11 as shown in FIG. 1:

First, the Ni lead 11 with a length of 50 mm, a width of 5 mm and athickness of 0.15 mm was prepared, and the surface thereof was washedwith aqua regia and then with pure water. A glass slurry comprising analumino-borosilicate glass frit and ethanol was applied onto the area ata distance of 30 to 35 mm from the bottom edge of the lead and thendried. This was calcined under Ar atmosphere at 900° C. to form a glasslayer with a thickness of 0.02 mm surrounding part of the Ni lead. Thislead was referred to as Sample 1.

Sample 2

The area at a distance of 30 mm or shorter and the area at a distance of35 to 40 mm from the bottom edge of a Ni lead treated by washing in thesame manner as with Sample 1 were covered with a tape. Subsequently, thelead was immersed into a 0.5 M Ni(NO₃)₂.6H₂O aqueous solution, which wasplaced between two Ni anode plates (50×10×0.15 mm) of a counterelectrode. A current of 50 mA was passed for 240 seconds between the Nilead as a cathode and the Ni anode plates, whereby Ni(OH)₂ was depositedon the whole area at a distance of 30 to 35 mm from the bottom edge ofthe Ni lead. After the tape was peeled, the lead was washed with waterto be dried and then calcined under Ar atmosphere at 900° C. to form aNiO layer with a thickness of about 0.02 mm on part of the lead. Thislead was referred to as Sample 2.

Sample 3

Onto the whole area at a distance of 30 to 35 mm from the bottom edge ofa Ni lead treated by washing in the same manner as with Sample 1, anethanol dispersion of polytetrafluoroethylene as a water repellent wasapplied so as to have a thickness of 0.02 mm. This lead was referred toas Sample 3.

Sample 4

Onto the whole area at a distance of 30 to 35 mm from the bottom edge ofa Ni lead treated by washing in the same manner as with Sample 1, anepoxy resin adhesive was applied so as to have a thickness of 0.02 mm.This lead was referred to as Sample 4.

Sample 5

Onto the whole area at a distance of 30 to 35 mm from the bottom edge ofa Ni lead treated by washing in the same manner as with Sample 1, anasphalt pitch-based sealing agent was applied so as to have a thicknessof 0.02 mm. This lead was referred to as Sample 5.

Evaluation

In the following procedure, a test apparatus as shown in FIG. 2 wasassembled:

First, a 31 wt % KOH aqueous solution 22 was poured into a beaker 21,and the area at a distance of 20 mm or shorter from the bottom edge ofthe lead 11 of Sample 1 was immersed into the aqueous solution 22.Alkali detection paper 24 was affixed onto the area at a distance of 35to 40 mm from the bottom edge of the lead 11.

Two Ni anode plates 25 (50×10×0.15 mm) were prepared and immersed intothe aqueous solution 22 so as to be interposed by the lead 11. Areference Hg/HgO electrode 26 was immersed into the aqueous solution 22.

A voltage was applied between the upper part of the lead 11 and theupper parts of the Ni anode plates 25 such that the electric potentialof the lead 11 became −0.9 V with respect to the reference electrode 26.The color tone of the alkali detection paper 24 was observed every 30minutes.

The same tests as above were conducted on Samples 2 to 5. Further, forreference, the same test as above was conducted on Sample 4 except thatthe voltage was not applied to the lead. The time elapsed from the startof application of the voltage to the color change of the alkalidetection paper 24 was shown in Table 1.

TABLE 1 Electric potential Time elapsed from start of of Ni lead voltageapplication to color Sample (V, vs. Hg/HgO) change (hr) 1 −0.9 >24 2−0.9 >24 3 −0.9 2 4 −0.9 3.5 — >24 5 −0.9 3

As shown in Table 1, with the voltage applied to the Ni lead, there wasobserved no color change of the alkali detection paper in Samples 1 and2 even after the elapse of 24 hours or longer. In Samples 3 to 5, on theother hand, the color changes of the alkali detection paper wereobserved after the elapse of 2 to 3.5 hours. It was thereby confirmedthat: in Samples 1 and 2, the alkaline aqueous solution did not ascendalong the Ni lead over the glass layer and the NiO layer, respectively;in Samples 3 to 5, the alkaline aqueous solution ascended along the Nilead over the water repellent layer, the epoxy resin adhesive layer andthe sealing agent layer, respectively. It should be noted that, inSample 4 and Sample 5 with the voltage applied thereto, separation ofthe epoxy resin adhesive layer and the sealing agent layer from the Nileads, respectively, were confirmed.

In Sample 4 where the voltage had not been applied to the Ni lead, therewas observed neither the color change of the alkali detection paper norseparation of the epoxy resin adhesive layer from the Ni lead. One ofthe causes of the significant difference in test results between thecase of applying the voltage to the Ni lead and the case of not applyingthe same is presumably that in the case of applying the voltage, thesurface tension of the alkaline aqueous solution decreased due to theelectrocapillary action. Another cause is presumably that an alkalineconcentration increased in the vicinity of the lead through reduction ofoxygen on the interface of three phases formed by the alkaline aqueoussolution, oxygen and the electrode, which led to the action of thedriving force in the ascent of the alkaline aqueous solution.

From the fact that the epoxy resin adhesive layer was separated from theNi lead in Sample 4 with the voltage applied thereto, it is consideredthat the alkaline aqueous solution ascended along the interface betweenNi and the adhesive while separating the adhesive layer from the surfaceof Ni. This is presumably because the affinity between Ni and thealkaline aqueous solution is higher than the affinity between theadhesive layer and Ni. It is considered that, also in Sample 5, thealkaline aqueous solution ascended along the interface between Ni andthe sealing agent.

The reason for the ascent of the alkaline aqueous solution in Sample 3with the voltage applied thereto was presumably that the weak bondingbetween the water repellent layer and the surface of the Ni leadfacilitated the ascent of the alkaline aqueous solution along theinterface between Ni and the water repellent. On the other hand, it wasthought that the chemical bonding between Ni and the insulating oxidelayer had been formed and that the alkaline aqueous solution was therebyunable to ascend along the interface between Ni and the insulatingoxide.

Sample 6

A Cu lead with a length of 50 mm, a width of 5 mm and a thickness of0.15 mm was prepared, and the surface thereof was washed with a 0.1 Nhydrochloric acid and then with pure water. After the whole area at adistance of 30 to 35 mm from the bottom edge of the lead was Co-platedby electroless plating to have a thickness of 5 μm, a glass slurrycomprising an alumino-borosilicate frit and ethanol was applied onto thesame area of the lead and then dried. This was calcined under Aratmosphere at 900° C. to form a glass layer with a thickness of 0.02 mmsurrounding part of the Cu lead. This lead was referred to as Sample 6.

Sample 7

After the whole area at a distance of 30 to 35 mm from the bottom edgeof a Cu lead treated by washing in the same manner as with Sample 6 wasCr-plated by electroless plating to have a thickness of 5 μm, a glassslurry comprising an alumino-borosilicate glass frit and ethanol wasapplied onto the same area of the lead and then dried. This was calcinedunder Ar atmosphere at 900° C. to form a glass layer with a thickness of0.02 mm surrounding part of the Cu lead. This lead was referred to asSample 7.

Evaluation

The same tests as those on Samples 1 to 5 were conducted.

As a result, no color change of the alkali detection paper was observedin Samples 6 and 7 using the Cu leads even after the elapse of 24 hoursor longer.

Next, the present invention was applied to a sealed battery:

EXAMPLE 1

A description will be given by reference to FIG. 3 and FIG. 4:

Two steel plates 31 with the surfaces thereof Ni-plated, each being in asubstantially square shape having a thickness of 0.1 mm and a side-widthof 50 mm with the four corners thereof chamfered to be an arc shape of aradius of 5 mm, were prepared, and the surface thereof was washed withaqua regia and then pure water. Subsequently, the four sides of thesteel plate 31 were immersed into a glass slurry comprising analumino-borosilicate glass frit and ethanol to be dried, which was thencalcined under Ar atmosphere at 900° C. to form a glass layer 32 with awidth of 5 mm and a thickness of 20 μm on the periphery of each of thetwo steel plates 31. The glass layer had a specific resistance of 10⁷Ω·cm.

Next, a nickel foam substrate was filled with a positive electrode pastecomprising water and an active material mainly composed of Ni(OH)₂ to bedried and pressed, which was then cut into a square shape with aside-length of 38 mm to obtain a positive electrode 41. The positiveelectrode 41 was placed on one of the steel plates 31 a. The thicknessof the positive electrode 41 was 0.55 mm.

As a negative electrode material, an MmNi₅ (Mm is misch metal) typehydrogen storage alloy (MmNi_(3.7)Mn_(0.4)Al_(0.3)Co_(0.6)) was used.This alloy was grinded to pass through a 360 mesh-sieve, and then addedwith an aqueous solution containing 1.5 wt % of CMC to obtain a negativeelectrode paste. The obtained negative electrode paste was applied ontoone face of the other steel plate 31 b to be dried. A redundant hydrogenstorage alloy was separated from the steel plate 31 b so as to make anegative electrode paste layer be a square with a side-length of 38 mm.The mixture layer was pressed to obtain a negative electrode 42. Thethickness of the negative electrode 42 was 0.33 mm.

An epoxy resin adhesive 43 was applied onto the glass layer 32 a of thesteel plate 31 a on the positive electrode side, and then a frame body44 made of polypropylene with a thickness of 1 mm was bonded to theglass layer. A sulfonated non-woven fabric made of polypropylene being asquare shape with a side-length of 39 mm, a basis weight of 66 g/m² anda thickness of 0.15 mm was placed as a separator 45 on the positiveelectrode 41. 0.65 mL of 31 wt % KOH aqueous solution was poured fromthereabove. Subsequently, the epoxy resin adhesive 43 was applied ontothe frame body 44, the steel plate 31 b was arranged such that theseparator 45 and the negative electrode 42 were mutually opposed, andthe frame body 44 was bonded to the glass layer 32 b of the steel plate31 b. The battery as thus fabricated was referred to as Battery A ofEXAMPLE 1.

EXAMPLE 2

Two steel plates with the surfaces thereof Ni-plated, each being in asubstantially square shape having a thickness of 0.1 mm and a side-widthof 50 mm with the four corners thereof chamfered to be an arc shape of aradius of 5 mm, were prepared, and the surface thereof was washed withaqua regia and then pure water. Subsequently, the 40 mm-square centralparts of both faces of each of the steel plates were covered with tapes.The steel plate covered with the tapes was immersed into a 0.5 MNi(NO₃)₂.6H₂O aqueous solution and placed between two Ni anode plates(70×70×0.15 mm) of a counter electrode. A current of 900 mA was passedfor 480 seconds between the steel plate as a cathode and the Ni anodeplates to deposit Ni(OH)₂on the four sides of the steel plate. Afterpeeling the tapes, the steel plate was washed with water and dried,which was then calcined under Ar atmosphere at 900° C. to form a NiOlayer with a width of 5 mm and a thickness of about 20 μm on the foursides of the steel plate. The NiO layer had a specific resistance of 10⁶Ω·cm.

Except that the NiO layer was arranged as an insulating oxide layer asthus described, a battery was fabricated in the same manner as inEXAMPLE 1. The obtained battery was referred to as Battery B of EXAMPLE2.

COMPARATIVE EXAMPLE 1

Except that the glass layer was not formed on the four sides of thesteel plate, a battery was fabricated in the same manner as inEXAMPLE 1. The obtained battery was referred to as Battery C ofCOMPARATIVE EXAMPLE 1.

Evaluation

Batteries A to C were each charged at a current of 0.1 C for 16 hoursand discharged at a current of 0.2 C until the battery voltage reached1.0 V, while being pressed with a pressing-jig in the thicknessdirection of the battery in order to suppress the expansion thereof.After the discharge, the periphery of each battery was wiped with alkalidetection paper to observe presence or absence of liquid leakage. Theresults are shown in Table 2.

TABLE 2 Battery Liquid leakage A None B None C Leaked

In Battery C of COMPARATIVE EXAMPLE 1 where the liquid leakage wasfound, separation of the epoxy resin adhesive from the periphery of thesteel plate on the negative electrode side was observed, while inBatteries A and B of EXAMPLES 1 and 2, such separation was not observed.It was thereby revealed that the electrolyte in the electrochemicaldevice can be sealed according to the present invention.

EXAMPLE 3

A description will be given by reference to FIG. 5:

A nickel foam substrate was filled with a positive electrode pastecomprising water and an active material mainly composed of Ni(OH)₂ to bedried and pressed, which was then cut into a rectangular shape with alength of 40 mm and a width of 9 mm to obtain a positive electrodeplate. The thickness of the positive electrode plate was 0.75 mm.

As a negative electrode material, an MmNi₅ (Mm is misch metal) typehydrogen storage alloy (MmNi_(3.7)Mn_(0.4)Al_(0.3)Co_(0.6)) was used.This alloy was grinded to pass through a 360 mesh-sieve, and then addedwith an aqueous solution containing 1.5 wt % of CMC to obtain a negativeelectrode paste. The obtained negative electrode paste was applied ontoboth faces of a steel plate having a thickness of 0.06 mm, withNi-plated and apertures arranged, to be dried and pressed, which wasthen cut into a rectangle with a length of 42 mm and a width of 10 mm toobtain a negative electrode plate. The thickness of the negativeelectrode plate was 0.45 mm.

Three positive electrode plates and four negative electrode plates wereprepared. A positive electrode lead 51 was welded to each of thepositive electrode plates and a negative electrode lead 52 was welded toeach of the negative electrode plates. Subsequently, each of thepositive electrode plates was wrapped with a sack-like separator made ofa non-woven fabric having a thickness of 0.15 mm and a basis weight of60 g/m², with potassium salt of polyacrylic acid applied thereonto. Asthe non-woven fabric used was made of sulfonated polypropylene.

The four negative electrode plates and the three positive electrodeplates wrapped with the separator were stacked alternately to constitutean element 53 for power generation. Three elements 53 for powergeneration were produced and each was inserted into a closed-bottomresin case 54 made of polypropylene. The elements for power generationaccommodated in the closed-bottom resin cases 54 were accommodated intoa metal case 55 three times larger than the closed-bottom resin case 54.

Meanwhile, a Ni lead with a length of 6 mm was prepared, and a glassslurry comprising an alumino-borosilicate glass frit and isopropanol wasapplied onto the central part of the Ni lead and then dried. This wascalcined under Ar atmosphere at 900° C. to form a glass layer 56 with athickness of 0.1 mm and a width of 2 mm in the central part of the Nilead to produce a connecting lead 57. The glass layer 56 had a specificresistance of 10⁷ Ω·cm.

A positive electrode lead 51 a of a predetermined element for powergeneration and a negative electrode lead 52 a of another predeterminedelement for power generation were welded to each other with a connectinglead 57, and by using two of the connecting lead 57, the three elementsfor power generation were connected in series. On the other hand, theother positive electrode lead 51 b and the negative electrode lead 52 bwere connected to predetermined parts of a sealing plate 58 having threeapertures for liquid pouring. The sealing plate 58 and the metal case 55were laser-welded to each other, and a 30 wt % KOH aqueous solution waspoured to each of the elements for power generation through the aperturefor liquid pouring.

A gasket 59 was engaged to one of the apertures for liquid pouring. Aniron rivet 510 was inserted in the aperture 512 a via the gasket 59 andfixed thereto with its bottom edge crimped to a washer 511. The positiveelectrode lead 51 b was connected to the washer 511 by resistancewelding. The negative electrode lead 52 b was directly connected to thesealing plate 58 also serving as a negative electrode terminal. Theaperture 512 a for liquid pouring was sealed with a positive electrodeterminal cap 514 having a rubber valve 513 by connecting the rivet 510with the cap 514 by resistance welding. The remaining two apertures 512b for liquid pouring were sealed by welding metal sealing plugs 515. Thesealed alkaline storage battery as thus fabricated was referred to asBattery D of EXAMPLE 3.

EXAMPLE 4

A Ni lead with a length of 6 mm was prepared and the both ends thereofwere covered with tapes. This lead was immersed into a 0.5 MNi(NO₃)₂.6H₂O aqueous solution and placed between two Ni anode plates(50×10×0.15 mm) of a counter electrode, and a current of 20 mA waspassed for 240 seconds between the Ni lead as a cathode and the Ni anodeplates to deposit Ni(OH)₂ on the central part of the Ni lead. This waswashed with water and dried, which was then calcined under Ar atmosphereat 900° C. to form a NiO layer with a thickness of about 0.02 mm in thecentral part of the Ni lead. The NiO layer had a specific resistance of10⁶ Ω·cm. Thereafter, the tapes at the both ends of the Ni lead wereremoved.

Except that the NiO layer was arranged as an insulating oxide layer asthus described, a battery was fabricated in the same manner as inEXAMPLE 3. The obtained battery was referred to as Battery E of EXAMPLE4.

COMPARATIVE EXAMPLE 2

Except that a normal Ni lead was used for the electric connectionbetween the elements for power generation, a battery was produced in thesame manner as in EXAMPLE 3. The obtained battery was referred to asBattery F of COMPARATIVE EXAMPLE 2.

COMPARATIVE EXAMPLE 3

Except that a film made of polypropylene (thickness: 0.1 mm) wasthermally adhered to the central part of the Ni lead, a battery wasproduced in the same manner as in COMPARATIVE EXAMPLE 2. The obtainedbattery was referred to as Battery G of COMPARATIVE EXAMPLE 3.

EXAMPLE 5

Except that a sulfonated non-woven fabric made of polypropylene was usedas it was as a separator instead of applying potassium salt ofpolyacrylic acid onto the separator, a battery was produced in the samemanner as in EXAMPLE 3. The obtained battery was referred to as BatteryH of EXAMPLE 5.

Evaluation

Batteries D to H were all sealed nickel-metal hydride storage batterieswith an operating voltage of 3.6 V and the theoretical battery capacityof each of the batteries was 500 mAh.

For the purpose of activating Batteries D to H, the batteries underwentfive cycles of charge/discharge. The pattern of one cycle was that thebattery was charged at a current of 0.1 C for 16 hours, put to aone-hour rest, discharged at a current of 0.2 C until the batteryvoltage reached 3.0 V and then put to another one-hour rest.

Next, the charge/discharge cycle life of each of the activated batteriesD to H was observed.

The pattern repeated herein was that the battery was charged at acurrent of 0.5 C up to 105% of the theoretical capacity, put to a30-minute rest, discharged at a current of 0.5 C until the batteryvoltage reached 3 V, and then put to another 30-minute rest. Every 50cycles, each of the batteries was charged at a current of 0.1 C for 16hours, put to a one-hour rest, discharged at a current of 0.2 C untilthe battery voltage reached 3 V and then put to another one-hour rest,to measure the capacity of the battery. The ratio of the dischargecapacity thus obtained to the initial discharge capacity was calculatedon percentage as a discharge capacity ratio. FIG. 6 shows the relationsbetween the discharge capacities and the number of the charge/dischargecycles.

Each of the batteries after the measurement of the capacity thereof inthe same manner as above was charged at a current of 0.1 C for 16 hours,stored under an atmosphere at 45° C. for two weeks, and then dischargedat a current of 0.2 C until the battery voltage reached 3 V. The ratioof the capacity of the battery after the storage to the capacity of thebattery before the storage was calculated on percentage as a capacitymaintenance ratio. FIG. 7 shows the relations between the capacitymaintenance ratios and the number of charge/discharge cycles.

It was found, as shown in FIG. 6 and FIG. 7, that there were drasticdecreases in discharge capacity ratios and capacity maintenance ratiosof Batteries F and G. The capacity maintenance ratio decreasedpresumably because the alkaline electrolyte crept on the lead connectingbetween the elements for power generation, and the electrolyte hencecaused a short circuit of the elements for power generation. Thedischarge capacity ratio decreased presumably because there was avariation in charged state between the elements for power generation dueto the short-circuit caused by the electrolyte andover-charge/over-discharge were thus repeated with some of the elementsfor power generation.

Next, drop tests were conducted on activated Batteries D to H in thefollowing procedure:

First, in the pattern that the battery was charged at a current of 0.1 Cfor 16 hours, put to a one-hour rest, discharged at a current of 0.2 Cuntil the battery voltage reached 3 V and then put to another one-hourrest, the capacity of each of the batteries was measured. Next, thebattery was charged at a current of 0.1 C for 16 hours, stored in aconstant temperature bath at 45° C. for two weeks, and after beingreturned to room temperature, discharged at a current of 0.2 C until thebattery voltage reached 3 V to measure the remaining capacity. The ratioof the obtained remaining capacity to the capacity before the storagewas calculated on percentage as a capacity maintenance ratio.

Subsequently, each of the batteries was dropped from a height of 50 cmonto a concrete floor six times so that six faces of the battery landedon the floor. These six times of drops were made to be one set andtotally ten sets of drops were conducted. The capacity maintenance ratioof the battery dropped was then calculated in the same manner as above.Table 3 shows the capacity maintenance ratios of the batteries beforeand after the drops.

TABLE 3 Capacity maintenance ratio Capacity maintenance ratio Batterybefore drop (%) after drop (%) D 75.1 74.8 E 75.3 74.9 F 70.3 65.3 G75.2 73.8 H 75.0 0.5

As shown in Table 3, in Battery H where potassium salt of polyacrylicacid as an agent for gel formation had not been applied onto theseparator, the maintenance ratio drastically decreased after the drop.This is presumably because, due to the shock of the drop, theelectrolyte was eluted from the separator and the electrode plate andtransferred between the elements for power generation, causing theshort-circuit therebetween. It was revealed from this result that it ispossible to provide a sealed alkaline secondary battery reliable againstthe shock, by applying the gel electrolyte to the present invention.

EXAMPLE 6

A nickel foam substrate was filled with a positive electrode pastecomprising water and an active material mainly composed of Ni(OH)₂ to bedried and pressed, which was then cut into a rectangular shape with alength of 27 mm and a width of 15 mm to obtain a positive electrodeplate. The thickness of the positive electrode plate was 0.8 mm.

As a negative electrode material, an MmNi₅ (Mm is misch metal) typehydrogen storage alloy (MmNi_(3.7)Mn_(0.4)Al_(0.3)Co_(0.6)) was used.This alloy was grinded to pass through a 360 mesh-sieve, and then addedwith an aqueous solution containing 1.5 wt % of CMC to obtain a negativeelectrode paste. The obtained negative electrode paste was applied ontoboth faces of a steel plate having a thickness of 0.03 mm, withNi-plated and apertures arranged, and then dried and pressed, which wascut into a rectangular shape with a length of 27 mm and a width of 15 mmto obtain a negative electrode plate. The thickness of the negativeelectrode plate was 0.45 mm.

Three positive electrode plates and four negative electrode plates wereprepared. A positive electrode lead was welded to each of the positiveelectrode plates and a negative electrode lead was welded to each of thenegative electrode plates. Subsequently, each of the positive electrodeplates was wrapped with a sack-like separator made of non-woven fabrichaving a thickness of. 0.12 mm and a basis weight of 60 g/m². As thenon-woven fabric used was made of sulfonated polypropylene. The fournegative electrode plates and the three positive electrode plateswrapped with the separator were stacked alternately to constitute anelement for power generation. The element for power generation wasaccommodated in a closed-bottom metal case.

Meanwhile, a steel plate 81 with a length of 34 mm, a width of 6 mm anda thickness of 0.4 mm was Ni-plated and an aperture 82 with a diameterof 2.8 mm was arranged in the center thereof. A glass slurry comprisingan alumino-borosilicate glass frit and isopropanol was applied onto thearea with a length of 20 mm and a width of 5 mm in the central part ofone face of the steel plate 81, and then dried. This was calcined underAr atmosphere at 900° C. to form a glass layer 83 with a thickness of0.1 mm on one face of the steel plate. The glass layer had a specificresistance of 10⁷ Ω·cm. A sealing plate 84 was thus produced. FIG. 8shows the front view (a) and the I-I line cross-sectional view (b)thereof.

The sealing plate 84 and the closed-bottom metal case accommodating theelement for power generation were laser-welded to each other such thatthe side of the glass layer 83 became an inter face, and a 30 wt % KOHaqueous solution was poured through the aperture 82. A gasket wasengaged to the aperture 82 as in EXAMPLE 3. An iron rivet was insertedinto the aperture 82 via the gasket and fixed thereto with its bottomedge crimped to a washer. The positive electrode lead was connected tothe washer by resistance welding. The negative electrode lead wasdirectly connected to the metal part of the sealing plate 84 alsoserving as a negative electrode terminal. As in EXAMPLE 3, the aperture82 was sealed with a positive electrode terminal cap having a rubbervalve by connecting the rivet with the cap by resistance welding. Thesealed alkaline storage battery as thus fabricated was referred to asBattery d of EXAMPLE 6.

COMPARATIVE EXAMPLE 4

Except that a glass layer was not arranged on the sealing plate, abattery was fabricated in the same manner as in EXAMPLE 6. The obtainedbattery was referred to as Battery e of COMPARATIVE EXAMPLE 4.

Evaluation

Batteries d and e were both sealed nickel-metal hydride storagebatteries with an operating voltage of 1.2 V, and the theoreticalbattery capacity of each of the batteries was 600 mAh.

For the purpose of activating Batteries d and e, the batteries underwentfive cycles of charge/discharge. The pattern of one cycle was that thebattery was charged at a current of 0.1 C for 16 hours, put to aone-hour rest, charged at a current of 0.2 C until the battery voltagereached 1.0 V and then put to another one-hour rest.

A heat cycle test was conducted by using 10 cells each of activatedBatteries d and e. In this test, the cycle of storage of the battery at65° C. for six hours and subsequent storage thereof at −10° C. for 6hours was repeated 60 times.

After completion of the test, there was observed presence or absence ofliquid leakage by wiping the periphery of the positive electrodeterminal with alkali detection paper. As a result, no liquid leakage wasobserved in the ten cells of Battery d, while the liquid leakage wasobserved in five cells out of the ten cells of Battery e.

EXAMPLE 7

A description will be given by reference to FIGS. 9 to 11:

Four steel plates 91 with the surfaces thereof Ni-plated, each being ina substantially square shape having a thickness of 0.1 mm and aside-width of 100 mm with the four corners thereof chamfered to be anarc shape of a radius of 5 mm, were prepared, and the surface thereofwas washed with aqua regia and then pure water. Subsequently, the foursides of the steel plate 91 were immersed into a glass slurry comprisingan alumino-borosilicate glass frit and isopropanol and then dried, whichwas calcined under Ar atmosphere at 900° C. to form a glass layer 92with a width of 5 mm and a thickness of 0.1 mm on the periphery of eachof the four steel plates. The glass layer had a specific resistance of10⁷ Ω·cm. The obtained steel plate was used as a bipolar currentcollector.

As a negative electrode material, an MmNi₅ (Mm is misch metal) typehydrogen storage alloy (MmNi_(3.7)Mn_(0.4)Al_(0.3)Co_(0.6)) was used.This alloy was grinded to pass through a 360 mesh-sieve, and then addedwith an aqueous solution containing 1.5 wt % of CMC to obtain a negativeelectrode paste. The obtained negative electrode paste was applied ontoone face of the bipolar current collector and then dried, and redundanthydrogen storage alloy was then separated so as to make the negativeelectrode paste layer a square with a side-length 85 mm, and pressed toobtain a negative electrode 93. The thickness of the negative electrode93 was 0.35 mm.

Next, a nickel foam substrate was filled with a positive electrode pastecomprising water and an active material mainly composed of Ni(OH)₂ andthen dried and pressed, which was cut into a square with a side-lengthof 83 mm to obtain a positive electrode 94. The positive electrode 94was placed in the central part of the other face of the bipolar currentcollector. The thickness of the positive electrode 94 was 0.55 mm.

Two sets of bipolar electrode plates having the positive electrode 94 onone face thereof and the negative electrode 93 on the other face thereofwere thus produced.

Further, one monopolar electrode plate having only the negativeelectrode 93 on one face of the bipolar current collector and onemonopolar electrode plate having only the positive electrode 94 on oneface of the bipolar current collector were prepared.

Next, 200 mL of 30 wt % KOH aqueous solution and 20 g of potassiumpolyacrylate having been passed through a 360 mesh-sieve were mixed andstirred, which was then defoamed under a reduced pressure to prepare agelated alkaline electrolyte.

Into the gelated alkaline electrolyte, a sulfonated non-woven fabricseparator made of polypropylene in a square shape with a side-length of88 mm (thickness: 0.2 mm, basis weight: 72 g/m²) was immersed and thendefoamed under a reduced pressure so as to make the gelated electrolyteimpregnated into the separator. The separator 95 with the electrolyteimpregnated therein was arranged on the positive electrode 94 of themonopolar electrode plate having only the positive electrode. Thebipolar plate was arranged thereon via the separator 95 such that thepositive electrode 94 and the negative electrode 93 were mutuallyopposed. This operation was repeated one more time. Thereon, themonopolar electrode plate having only the negative electrode 93 wasarranged via the separator 95 such that the positive electrode 94 andthe negative electrode 93 were mutually opposed. A frame body 97 made ofpolypropylene with a thickness of 1.1 mm was interposed between theglass layers 92 of the adjacent current collectors via an epoxy resinadhesive 96. Finally, the adhesive 96 was cured by heat to obtain asealed electrode plate assembly 98.

A negative electrode lead 102 and a positive electrode lead 103 wereconnected to the negative electrode 93 and the positive electrode 94,respectively, on the outermost side of the electrode plate assembly 98.

Thereafter, the electrode plate assembly 98 was covered with a heatshrinkable film and inserted into a closed-bottom metal case 111. Thenegative electrode lead 102 was then welded to a sealing plate 112.Further, the positive electrode lead 103 was welded to a positiveelectrode terminal 113 equipped with a safe valve. The positiveelectrode terminal was arranged on the sealing plate 112 via aninsulating material. The sealing plate 112 and the open-end of the case111 were welded to each other by laser-welding to complete a bipolarnickel-metal hydride storage battery. This battery was referred to asBattery I of EXAMPLE 7.

EXAMPLE 8

Except that the gap between glass layers each arranged on the peripheryof each of the bipolar current collectors was not sealed with a framebody and an epoxy resin adhesive, a bipolar nickel-metal hydride storagebattery having an electrode plate assembly 98 a as shown in FIG. 12 wasfabricated in the same manner as in EXAMPLE 7. This battery was referredto as Battery J of EXAMPLE 8.

EXAMPLE 9

Except that a 30 wt % KOH aqueous solution was singly used as anelectrolyte in place of the gelated electrolyte, a bipolar nickel-metalhydride storage battery as shown in FIG. 9 was fabricated in the samemanner as in EXAMPLE 7. This battery was referred to as Battery K ofEXAMPLE 9.

COMPARATIVE EXAMPLE 5

Except that a glass layer was not arranged on the periphery of eachbipolar current collector, a bipolar nickel-metal hydride storagebattery was fabricated in the same manner as in EXAMPLE 7. This batterywas referred to as Battery L of COMPARATIVE EXAMPLE 5. A frame body madeof polypropylene with a thickness of 1.1 mm was interposed between theperipheries of adjacent current collectors via an epoxy resin adhesive.

COMPARATIVE EXAMPLE 6

A description will be given by reference to FIG. 13:

Four steel plates 131 with the surfaces thereof Ni-plated, each being asquare having a thickness of 0.1 mm and a side-width of 100 mm, wereprepared. A polypropylene resin layer 132 was arranged on the peripheryof the four sides by injection molding. Thereafter, Apolytetrafluoroethylene resin dispersed in ethanol was applied onto aninner angle part where the face of the steel plate and the resin layer132 crossed at right angle, to form a water repellent layer 133 whichwas a substantially triangle in cross section. By this means, the steelplate 131 with the insulating resin layer 132 and water-repellent layer133 attached to the periphery thereof was used as a bipolar currentcollector, while an epoxy resin adhesive was not used. Further, a 30 wt% KOH aqueous solution was impregnated into the separator. Except that,a bipolar nickel-metal hydride storage battery was fabricated in thesame manner as in EXAMPLE 7. This battery was referred to as Battery Mof COMPARATIVE EXAMPLE 6. Battery M corresponds to the battery disclosedin Japanese Patent Publication No.2623311.

COMPARATIVE EXAMPLE 7

A description will be given by reference to FIG. 14 illustrating part ofan electrode plate assembly in the production process:

Four steel plates 141 with the surfaces thereof Ni-plated, each being asquare having a thickness of 0.1 mm and a side-width of 100 mm, wereprepared. To the periphery of the four sides of each plate, an ethanoldispersion including a silica powder and a polytetrafluoroethylenepowder was applied. The steel plate was used as a bipolar currentcollector. A 30 w % KOH aqueous solution was impregnated into aseparator 143. As a positive electrode 144 and a negative electrode 145,the same ones were used as in EXAMPLE 7. An electrolyte impermeable andgas permeable resin composition 142 with a thickness of 1.5 mm wasprovided between the peripheries of the bipolar plates. Except that, anelectrode plate assembly was produced in the same manner as in EXAMPLE7. Subsequently, the electrode plate assembly was heat-pressed to adherethe resin composition 142 and the steel plate 141 so that the currentcollectors were bonded to each other. In the same manner as in EXAMPLE7, a bipolar nickel-metal hydride storage battery was fabricated. Thisbattery was referred to as Battery N of COMPARATIVE EXAMPLE 7. Battery Ncorresponds to the battery disclosed in Japanese Patent PublicationNo.2993069.

Evaluation

Batteries I to N were all nickel-metal hydride storage batteries with anoperating voltage of 3.6 V, and the theoretical capacity of each batterywas 600 mAh. For the purpose of activating Batteries I to N, thebatteries underwent five cycles of charge/discharge. The pattern of onecycle was that the battery was charged at a current of 0.1 C for 16hours, put to a one-hour rest, discharged at a current of 0.2 C untilthe battery voltage reached 3.0 V and then put to another one-hour rest.

Next, the charge/discharge cycle life of each of the activated BatteriesI to N was measured. The pattern repeated herein was that the batterywas charged at a current of 0.5 C up to 105% of the theoreticalcapacity, put to a 30-minute rest, discharged at a current of 0.5 Cuntil the battery voltage reached 3 V, and then put to another 30-minuterest. Then, the number of the cycles until the discharge capacity became70% of the initial capacity was counted. The results were shown in Table4.

TABLE 4 Battery Number of charge/discharge cycle (time) I 235 J 378 K228 L 38 M 73 N 67

As shown in Table 4, the cycle lives of Batteries L, M and N were veryshort. This is presumably because insufficient prevention of creeping ofthe electrolyte due to the electrocapillary action leads to a shortcircuit between the cells, resulting in variation in charged state ofthe cell. On the other hand, in Batteries I to K where the insulatingoxide layer was arranged on the periphery of the bipolar currentcollectors, the insulating oxide layer effectively prevented thecreeping of the electrolyte, resulting in obtainment of a favorablecycle life.

Next, drop tests were conducted on Batteries I to N after theactivation, in the same manner as in the drop tests on Batteries D to H.The capacity maintenance ratios of the batteries before and after thedrops were shown in Table 5.

TABLE 5 Capacity maintenance ratio Capacity maintenance ratio Batterybefore drop (%) after drop (%) I 80.5 80.2 J 80.1 75.2 K 80.3 23.8 L23.2 0 M 68.7 10.3 N 63.4 15.4

As shown in Table 5, the capacity maintenance ratios of Batteries L, Mand N were considerably low even before the drop process. This ispresumably because a short circuit between the cells caused by theelectrolyte intensified the self-discharge.

Battery K demonstrated a favorable capacity maintenance ratio before thedrop, but it largely decreased after the drop. This is presumablybecause the epoxy resin sealing the cell was separated from the bipolarcurrent collectors due to the shock of the drop, and the creeping of theelectrolyte occurred. On the other hand, the capacity maintenance ratiosof Batteries I and J remained favorable before and after the drop.

As apparent from the above description, according to a preferableembodiment of the present invention, it is possible to provide areliable electrochemical device with liquid leakage suppressed. Also,according to a preferable embodiment of the present invention, it ispossible to provide a low-cost, reliable sealed alkaline storagebattery. Further, according to a preferable embodiment of the presentinvention, it is possible to provide a low-cost, long-life, reliablebipolar alkaline storage battery.

Although the present invention has been described in terms of thepresently preferred embodiments, it is to be understood that suchdisclosure is not to be interpreted as limiting. Various alterations andmodifications will no doubt become apparent to those skilled in the artto which the present invention pertains, after having read the abovedisclosure. Accordingly, it is intended that the appended claims beinterpreted as covering all alterations and modifications as fall withinthe true spirit and scope of the invention.

1. A sealed electrochemical device comprising at least two elements forpower generation and at least one lead for electrically connecting saidat least two elements for power generation, wherein each of saidelements for power generation is not sealed and each comprises anelectrolyte and at least one electrode plate; said at least one leadelectrically connects said at least two elements for power generationthat are not sealed; said electrolyte comprises a solute and a solventdissolving said solute; and said lead has an insulating oxide layer forpreventing said electrolyte from creeping on at least part of thesurface of said lead.
 2. The sealed electrochemical device in accordancewith claim 1, wherein said electrolyte is in liquid form or gelatedform, said solute comprises an alkali metal hydroxide, and said solventcomprises water.
 3. The sealed electrochemical device in accordance withclaim 1, wherein said insulating oxide layer has a thickness of 10 μm ormore and 200 μm or less.